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Glycoligands Tuning the Magnetic Anisotropy of Ni II Complexes
Author(s) -
Charron Gaëlle,
Bellot François,
Cisnetti Federico,
Pelosi Giorgio,
Rebilly JeanNoël,
Rivière Eric,
Barra AnneLaure,
Mallah Talal,
Policar Clotilde
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601560
Subject(s) - chemistry , coordination sphere , anisotropy , intramolecular force , crystallography , hydrogen bond , electron paramagnetic resonance , magnetic anisotropy , pyridine , magnetization , intermolecular force , stereochemistry , nuclear magnetic resonance , molecule , crystal structure , physics , magnetic field , quantum mechanics , organic chemistry
Two organic ligands based on a sugar‐scaffold derived from galactose and possessing three O‐CH 2 ‐pyridine pendant arms at the 3‐, 4‐, and 5‐positions of the galactopyranose that act as chelates afford mononuclear complexes when reacted with a Ni II salt. The magnetization behavior in the form of M =f( H/T ) plots suggests the presence of appreciable magnetic anisotropy within the two complexes. The analysis of the EPR spectra performed at two different temperatures (7 and 17 K) and at three frequencies (190, 285, and 380 GHz) leads to the conclusion that the anisotropy has a high degree of axiality ( E / D =0.17 for the two complexes), but with a different sign of the D parameter. The spin hamiltonian parameters D and E were reproduced for the two complexes by using calculations based on the angular overlap model (AOM). The structural difference between the two complexes responsible of the sign of the D parameters was also determined using AOM calculations. A thorough analysis of the structures showed that the structural differences in the coordination sphere of the two complexes responsible of the different D parameter sign result from the nature of the sugar scaffolds. In complex 1 , the sugar scaffold imposes an intramolecular hydrogen bond with one of the atoms linked to Ni II ; this arrangement leads to a distorted coordination sphere and positive D value, while the absence of such a hydrogen bond in complex 2 leads to a less distorted environment around the Ni center and to a negative D value.